Ruby appers to take rather unique approach to parsing numeric literals, by allowing sign to be a part of the literal, unless it's separated by a whitespace:

mirb - Embeddable Interactive Ruby Shell
> -1.abs # same as (-1).abs, Integer#-@ is not called
 => 1
> - 1.abs # same as -(1.abs), Integer#-@ is called
 => -1

Whereas in e.g. C++:

There are no negative integer literals. Expressions such as -1 apply the unary minus operator to the value represented by the literal, which may involve implicit type conversions.

or in Python:

>>> -1 .__abs__()
-1
>>> - 1 .__abs__()
-1

I could not find any documentation regarding this (the official documentation only contains non-negative numbers as examples), and I'm curious about the rationale behind such design.

I'm mainly wondering which approach I should be taking in my own toy language. I think I like Ruby's way better, but I'd like to know possible pros and cons I may be missing.